Multiplex signaling system



Oct. 5,1926. 1,6013% H. NYQUIST MULTIPLEX SIGNALING I SYSTEM o i i l Filed Feb. 29 92 3 Sheets-Sheet 1 nws n IN VEN TOR ny wz A TTORNEY Oct. 5', 1926. 1,601,808

H. NYQUIST I MULTIPLEX SIGNALING SYSTEM Original Filed Feb. 29 I 192 3 Sheets-Sheet 2 4 if. b/ki qay By W ATTORNEY Oct. 5 1926. 1,601,808

H. NYQUIST MULTI PLEX S IGNALING SYSTEM Original Filed Feb. 29 1924 a Sneaks-Sheet 125'4'7 (1254' Zm I? IN VEN TOR .A TTORNE Y Patented Oct. 5, 1926."

UNITED STATES PATENT OFFICE.

HARRY NYQUIST, OF JACKSON HEIGHTS, NEW YORK, ASSIGNOR TO AMERIGAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MULTIPLEX SIGNALING SYSTEM.

Application filed February 29, 1924, Serial No. 696,048. Renewed March 18, 1826.

The principal object of my invention is to provide a new and improved method and suitable apparatus for utilizing a line for the simultaneous transmission of a number of messages. Another object of my invention is to provide for a system of mult plex telegraphy with discrimination by d fference of phase between messages in the same frequency range. Still another ob ect of my invention relates to providing for magnitude discrimination as well as for phase discrimination between different messages transmitted within the same frequency range. Other objects of my invention have to do with providing for accurate synchronization at the transmitting and receiving ends by means of a pilot channel; for regulating the absolute magnitude of the received signals so as .to facilitate magnitude (118 crimination; for phase adjustment between the sending and receiving ends to facilitate phase discrimination; and for relative phase adjustment in the different frequency ranges.

These and various other objects of my invention will become apparent on consideration of a limited number of specific examples of practice according to the invention, which I have chosen to illustrate and describe in this specification. With the understanding that the following specification is a disclosure of these particular examples of the invention and that the scope of the invention will be indicated in the appended claims, I now proceed to describe the structure and operation of the apparatus shown in the drawlngs.

Figure 1 is a diagram of multiplex sending equipment; Fig. 2 is a diagram of the corresponding receiving equipment; Fig. 3 is a diagram of a sending and receiving equipment with provision for automatic phase adjustment; Fig, 4 is a. diagram of a station at the opposite end of the lines from the station of Fig. 3; Fig. 5 is a diagram of.

a detail modification in Fig. 1; Figs. 6 and 7 are vector diagrams that will be referred to in explaining operation of the apparatus shown in the other figures, and Fig. 8 is a modification corresponding to the upper part of Fig. 2.

At the station West shown in Fig. 1, the constant speed motor M drives the inductor alternators, of which three are shown, G Gr and G of difierent carrier current generator Gr goes over the circuit 21-22-- 23-24 through an inductance coil of impedance y'n, a resistance 11. and a condenser of impedance y'n in series, where n has any suitable value, say 600 ohms. The value a is the resistance of the generator G looking into it across the points 21, 24 and it is important in the particular example illustrated that the impedance of the generator should be substantially a pure resistance as seen from its output terminal. The network 21 222324 is a balanced VVheatstone bridge because the product of the. impedances of one pair of opposite arms is equal to the corresponding product for the other pair of opposite arms, Hence ther is no interference in the transformer winding 37 due to electromotive force in the winding 38, nor vice versa. This is true for the particular frequency of the generator G It is also true for other frequencies because with a variation of frequency the impedance of The currents in the windings 37 and 38 are 90 degrees apart in phase. To prove this, notice that if a given voltage is impressed across the points 21 and 23, the current into the generator will lead by 45 degrees. The design is such that the impedance across the terminals of the coil 37 is effectively a pure resistance This being the case, it follows that the current in the winding 37 due to a voltage from the generator G, will lead by 45 degrees. Similarly, it can be shown that the current due to the generator Gr in the winding 38 will lag 45 degrees, and hence the currents in the windings 37 and 38 are 90 degrees apart.

Thus far it hasbeen assumed that the resistance of the coil marked with the impedance value +jn is negligible. Fig. 5 is a modified diagram to take care of the case frequencies. The output current from the when the resistance of this coil is not neglectzed. Assume that its resistance is p and associate another coil with a close inductive coupling whose self-inductance is the same and whose resistance is g. Then with the modified impedance values written on Fig. 5, it may readily be shown that the bridge is in balance as before. I

To ex lain the operation of the keys K and K 1n Fig. 1, first assume that the keys and the resistances 31 and 32 are removed 1 when two unequal resistances are joined it is permissible and often convenient to look at the point of junction as a point of reflection and to consider that there is a reflected current wave at the point of junction. In the case here under consideration, the reflected wave from point 27 is transmitted in part into the line. It is also well known that in the limiting case when one of the resistances is made zero and the other is left finite the reflected current is equal to and in phase with the incident current,

whereas in the limiting case when one of the reslstances 1s made infinite and the other 1s made finite the reflected current is equal to and in phase opposition to the incident current. If, therefore, the impedance at 27 is changed f"0m zero to infinity the effect is to reverse the current transmitted to the line. Now if a resistance artificial line is connected between point 27 and the point of reflection and 'if this artificial line is so designed that there is no reflection at point 27, then the incident wave will traverse the network and be attenuated, moreover, the reflected wave. will traverse the line also.

The net result of the artificial line is that the. current transmitted to the transmission line is attenuated by twice the loss of the artificial line. While the function of the key K is to open and close the circuit and thus to reverse the phase of the transmitted current, the function of key K is to add or remove artificial line and thus to change the magnitude without changing the phase.

Thus it will be seen that the key K transmits by phase reversal of the carrier current and the key K transmits by changing the magnitude of one component of the carrier current from generator G In a similar manner, the keys K and K respectively, transmit by phase reversal and magnitude change in the other carrier current component WhlCh differs 90 degrees in phase from that controlled by the keys K and K These two carrier current components of the same frequency, difl'ering 90 degrees in phase and varying in magnitude as determined by theoperation of the keys K and K, are superposed in the input of the band filter F whose output goes in multiple with the outputs from other'similar filters to the line Z These filters are confluent band filters each with relatively narrow band width and with the carrier frequency near the middle of its range so as to produce no serious phase shift during the building up of the signals. The currents to the line l, are amplified by the amplifier A,.

The box S represents a network similar to that between the generator Gr and the filter F Accordingly, four more messages will be carried in the channel from the generator Gr through the network S and the filter F and added in multiple on the line 2,.

Alternating current of still another frequency from the generator G, is passed through the artificial line or network N, by which it is reduced to the proper intensity to be put on the line. The simple unmodulated current of desired intensity goes from the network N through the filter'F and fermzinal repeater or amplifier A to the As shown in Fig. 1, three frequency channels are provided in the line Z,. Two of these, identified respectively, with the generators Gr and G each carry four messages. The frequency .in the third channel, identified with the generator G maybe called a pilot frequency and the channel may be called a pilot channel. As will be pointed out presently, this channel is utilized to provide for synchronism at the receiving end.

Referring to Fig. 2, this shows the receiving station which may be called East.. The currents coming in over the line Z pass through the adjustable artificial line or network N which is controlledautomatically in a manner to be described presently, This network N attenuates the currents so as to give a uniform magnitude in its output for the same signal elements from one time to another. The currents, thus attenuated to a standard magnitude, pass through the amplifier or terminal repeater A to the filters F',, F',, and F 3 in multiple. These filters correspond in their frequency ranges, respectively, with the filters F,, F 2 and F at station West.

The current of pilot frequently goes through the filter F to the amplifier A and thence to a power tube amplifier A, whose output goes to the synchronous motor SM. This motor drives the two generators Gr and G, of the same frequency, respective. as G, and Gr at station West.

The voltmeter relay V-is connected across the output from the amplifier A and normally holds its index at a certain position I the other to adjust the attenuation there- Thus it will be seen that by means of the voltmeter relay V and the associated apparatus, the current of pilot frequency is kept at uniform voltage-as delivered to the input. of the amplifier A This insures that through.

for the same signal elements in the other channels, the voltages delivered to the input of the amplifier A will be uniform. Even if the attenuation onthe line Z varies from time to' time, as may be the case due to weather conditions, etc-.. there will be no corresponding variation of the current and voltage magnitudes 1n the output from the network N at station East. If the reccived currents at East were to vary from time to time, it might happen that signals of lowmagnitude would sometimes be strong enough to affect the high magnitude receiving apparatus, or that high magnitude would sometimes be too weak toaffect the high magnitude receiving apparatus. By the adjustment at N, any such outcome is prevented. I

The modulated current of carrier frequently determined by the generator G at station"VVest will, accordingly. find its way through the filter F, and the potentiometer to the primary of the transformer whose secondary is 57 with an intermediate tap at 56.

Current of the same frequency as the carrier frequency in the channel considered will be generated locally by the generator Gr whose output is applied across the points 51 and 52. The network between these two points is associated with the ad justable taps 53 and 54 so that at these taps an electromotive force of the rope-r phase and intensity may be drawn of? and applied through the resistance a and the condenser. of impedance value -jn in series therewith. The electromotive forces across the resistance n and the condenser will 'be 90 degrees apart. Thus there will be applied to the grids of the generated electromotive force from the terminals of the resistance a of the same or opposite phase with the received carrier current component controlled by keys K and K and there will be applied to the grids of the detectors D and D, locally generated electromotive force from the terminals of the condenser whose impedance value is 7'n, of the same phase as the receiver carrier current component controlled by the detectors D and D locally keys K and K The electromotive forces due tothese received carrier current components will be. superposed in the secondary windings 5556 and 55-57 on the locally generated electromotive force.

Let the voltage on and D due to the generator Gr be reprethe grids of tubes D sented by the vector OX inFig. 6.- The superposed electromotive force due to the received currents on the line will comprise two components 90 apart. One of these will be 012 when both keys K and K are markmg a O12 when key K is marking and key K is spacmg O1'2 when key K is spacing and key K is marking O12' when both keys are spacing (As will be seen, unprimed numerals'are used when the corresponding detectors are markingQprimcd when they are spacing). Similarly, keys K and K, will determine a component O34, O'-3'4, 0-34 or 0-34'. These two components, combined with the 10- cally generated electromotive force OX give one of 16 different resultants from O to a point which may readily be identified by the notation on Fig. 6. For example, when all four keys are marking the resultant is the vector from O to the point 1234; for another example, when all four keys are spacing the resultant is the vector from O to the point 123'4'. It will be seen that four substantiallyv different vector magnitudes may be put on each of the detectors D and 1),. These may be classed as lying in the four zones 12, 12', 1'2 and 1'2, as shown in Fig. 6. Detector D and its associated elements of apparatus are adjusted so that when the grid voltage has the magnitude OX of Fig. 6, the core of the polar relay PB will be substantially deenergized. But when key K is marking whatever the condition of the other keys K K and K the resultant electromotive force on the grid of detector D will have a magnitude greater than OX and the polar relay PR controlled by detector D, will be on the marking side. On the other hand, when key K is spacing, whatever the condition of the other three keys, the resultant electromotive force on the grid of detector D will be of magnitude less than OX and the relay PR will be on the-spacing side.

The relay NR is a neutral relay and is adjusted to be marginal in its operation. The adjustments of this relay NR and the associated detector D and their circuits are such that the relay NR is deenergized when the voltage on the grid of the corresponding detector D has the magnitude OX in Fig. 6. When the magnitude of thisvoltage changes either way, the magnetism in the core of relay NR departs correspondingly one way or the other from zero. Because of its marginal character the relay NR will not operate for a change of voltage to zone 12' or to zone 1'2', but it will operate for a change to zone 12 or zone 1'2. Its armature is made slow enough in release so that on a reversal of the magnetism in the core it will not drop; in other words, the armature of the relay NR will not drop for a change in the key K,, by which the grid voltage goes from one to the other of zones 12 and 1'2.

To recapitulate briefly, key K, causes shifts between zones 12 and 12 on the one hand and zones 1'2 and 1'2 on the other hand and actuates polar relay PR, accordingly, whereas key K causes shifts between zones 12 and 1'2 on the one hand and zones 12' and 1'2 on the other hand, and operates neutral relay NR accordingly. The operation of detectors D and D and their corresponding relays is closely similar 'to that described for detectors 1), and I) and their relays and need not be repeated in detail.

Fig. 8 shows a modification of the part of Fig. 2 associated with filter F and generator G',. In this case the functions of the pair of detectors D, and D are performed by the'single detector I), and similarly 1),,

takes the place of D and D The system of Figs. 1 and 2 is adapted for operation in a case in which the phase shift involved in transmission over the line Z, is substantially the same from time to time. This being the case, adjustment made by the taps 53 and 5-1 will be lasting and will not have to be changed from time to time. In case the properties of the line are such that the phase shift over the line changes from time to time, the system shown in- Figs. 3 and 4 may be employed. At station West shown in Fig. 3, the constant speed motor M, the generators G,,. G and G the adjustable network N, the sending networks S and S and the respective filters F,, F and F are the same as for Fig. 1. Interposed between each generator G,, G, or G and the respective network N, S or IS is an adjustable phase shifter P,, P or In the system of Figs. 3 and 4, two lines are employed, Z, for transmitting from west to east and Z for transmitting from east to west. These may be the wires of a four- 'wire system. Reception at the station East on the line Z, is the same as explained heretofore for Fig. 2, and the upper part of Fig. 4 is the same as Fig. 2 with the addition that branch circuits in multiple are taken from the output of the filter F and from the outputs of the generators G'2 and G as will now be explained.

The output from the filter F, is the pilot received from the line 2,. This goes through the sending filter F and back from east to west over the line 1,. The branch circuits fro-m the generators Gr and Gr go, respectively, to the sending networks S, and S and the respective filters F and F to the line Z from eastto .west. Thus it-will be seen that the apparatus at the lower part of Fig. 4 is very similar to that of Fig. 1, the pilot carrier frequency current being that received from station West on the line Z, and sent back over line 1,.

At station West shown in Fig. 3, the incoming currents on the lineZ are adjusted automatically for magnitude in the adjustable network N" by the voltmeter relay V and associated apparatus like that shown in the lower part of Fig. 2. The received pilot frequency current not only goes to the vc-ltmeter relay V but a multiple branch carries this same frequency to the primary of the transformer 61 whose secondary is connected to apply the resulting electromotive forces alike to the grids of the two threeelectrode vacuum tube detectors 62 and 63.

The output from the pilot frequency G, goes from a branch circuit through the phase shifter P, to the primary of the transformer 64 and develops an electromo tive force which is applied in opposite phase to the grids of the two three-electrode vacuum tube detectors 62 and 63. The normal adjustment of the phase shifters P, and P, will be such that the electromotive forces developed in the secondaries of the transformers and 64 will be 90 degrees apart. Accordingly, under such normal conditions, the full line vector diagram of Fig. 7 will apply. On one rid, the electromotive force will be OY the sum of OX and KY. On the other grid, it will be OY', the sum of OX and X'Y'.

But suppose there is a slight departure from the 90-degree relation between the two electromotive forces in the s'econdaries'of the transformers 61 and 64. vThe vector diagram shown in dotted lines in Fig. 6 will then obtain and the electromotive forces on the grids of the two tubes 62 and 63 will become, respectively, OZ and OZ.

lVhen .the electromotive forces on these grids were equal, namely OY and OY', the output currents of the detectors 62 and 63 were equal and hence the armature of the relay 65 stood at neutral. But With the unequal electromotive forces OZ and OZ'on the grids of the two tubes, the output currents are unequal and the armature of the relay 65 will close on one contact or the other, energizing one or the other of the magnets 66 and 67. The result will be to push the wheel 68 against one side or the other of the yoke 69. This wheel 68 is turned constantly by the motor M" so that the cams 70 are shifted to the right or the left. These cams engage respective rollers which are mechanically concarrier current frequency, the currents are made to arrive at the receiving apparatus in proper phase relation with the locally generated currents. A

I claimL -1. Inacarrier current telegra h system, the method of transmitting apihrality of messages on each frequency, which consists in establishing two currents of that frequency in quadrature and modulating each current by phase reversal for one message and by magnitude change for another,

whereby four messages Wlll be carried on a current of one frequency.

2. In a multiplex carrier current system, means to generate two currents of the same frequency 90 apart, means to modulate each of these currents in two ways according to respective messages, and means to superpose the modulated currents on the line.

3. In a carrier current telegraph transmission system, means to generate two component currents of each frequency 90 apart and to modulate each of these components by phase reversals for one message and by magnitude changes for another and to put these modulated currents on the transmission line, means at the receiving station to generate currents 90 apart corresponding in with the carrier components, two detectors at the receiving station to which one locally generated current of the carrier frequency is applied and two other detectors to which the other component of that frequency is applied, polar relays associated respectively with one of each pair of detectors and neutral relays associated respectively with the other detector of each pair. a

4. In a multiplex carrier current system, means for""generating carrier currents 0 various frequencies and superposing them upon a transmission line, means to modulate all of these carrier currents except one in accordance with messages to be transmitted and phase adjusting means controlled by the unmodulated carrier component. I

5. In a multiplex carrier current transmitting system adapted for two-way transmission, means to generate a plurality of currents of different frequencies and to frequency and phase modulate them according to messages and put them on the transmission line, means to generate another current of another frequency and send it over the line one way and back the other way, means at the generatlng station to compare this current in phase before and after the two-way transm1ss1on,'and phase shifters associated with all the generators controlled by said comparing means.

The method of maintaining definite phase relations among the alternating currents of various frequencies in a multiplex carrier current system, which consists in appropriating one channel each way to an unmodulated current of a particular frequency, sending that current over the line and back and adjusting the phase in each channel as determined by the phase displacement in the channel of unmodulated current referred to.

7 The method of transmitting four mes sages on one frequency of carrier current, which consists in transmitting two current components of that frequency 90 degrees apart in phase, and modulating each component by phase reversal for one message and by magnitude change for another, whereby four messages will be carried on current of the one frequency.

8. In a carrier current system, means to generate two component currents of the same frequency 90 degrees apart in phase and to modulate each of them in two ways and put them on a line, means at the receiv mg end to generate two currents locally agreeing in frequency and phase with the said carrier components and to combine them therewith, and detectors respectively responsive to the current of each phase and also to the currents as modulated in each of the difierent ways at the sending station.

9. In a carrier current system, receiving means for a carrier-current of two components 90 degrees apart each modulated by phase reversal for one message and by mag nitude change for another message, said receiving system comprising means to generate two currents locally each agreeing with one of the carrier components in phase, two pairs of detectors to all of which the received currents from the line are applied and to which the locally generated'eurrents are applied in respective pairs, neutral relays res ectively associated with one detector 0 each pair and polar relays respectively associated with the other detector of each pair.

10. In a multiplex carrier current system,

means for generating carrier currents of various frequencies and superposing them on a transmission line, means to modulate the currents of each frequency with a plurality of messages, a receiving station, means at the receiving station to generate of pro agation on the ine.

11. n a multiplex carrier current system, phase shifters, means to compare a current before and after transmission to test changes in the phase displacement on the line, and

means automatically to adjust said phase shifters to compensate therefor.

12. In a two-Way multiplex carrier current transmission system, means to generate and transmit unmodulated current of one frequency once to and fro, means to compare the input and output currents of this frequency, and phase adjusting means automatically actuated by said comparing means.

13. The method of compensating for variation of phase relations in a multiplex carrier current system, which consists in transmitting unmodulated current of one frequency once to and fro, comparing its input and output for phase, and adjustin the phase for all frequencies by means of this comparison.

14. Means to compensate for variation of phase relations in a multiplex carrier current system, comprisin means to transmit unmodulated current of one frequency once to and fro, means to compare its input and output for phase, and phase adjusters for all frequencies controlled by said phase comparing means.

15. The method of regulating the phase and magnitude of the currents in a multiplex carrier current signaling system which consists in applying the carrier current of one particular frequency to make automatic adjustments for phase and magnitude of the currents of the other frequencies.

16. In a multiplex carrier current signaling system, means to transmit carrier currents of various frequencies, means to modulate certain of them and to detect such modulations, and means governed by the current of one particular frequency toeffect automatic adjustment of the phase and magnitude of the currents of other frequencies.

17. In a multiplex carrier current signaling-system, an adjustable phase shifter, and automaticmeans to adjust said phase shifter to compensate for variations of phase shift in transmission from time to time.

18. In a multiplex carrier-current signaling system, means to test one component of the current for phase shift, and an adjustable phase shifting network governed by said means.

19. In a multiplex carrier current signaling system having channels of different frequency, means to separate out the current of one frequency, means to test this current for phase shift, and an adjustable phase compensating network controlled by said means.

20. In a multiplex carrier current signaling system, means for generating carrier currents of various frequencies and superposing them upon a transmission line, means to modulate at least several of these carrier currents in accordance with messages to be transmitted, and hase adjusting means com trolled by one of the said carrier currents.

21. The method of maintaining definite phase relations among the alternating currents of various frequencies in a multiplex carrier current signaling system, which consists in sending the carrier current of one frequency over the line and back and adjusting the phase at each frequency as'determined by the phase displacement of the carrier current of the one frequency referred to.

22. In a two-way multiplex carrier current transmission system, means to generate and transmit currents of various frequencies and to transmit one of these currents once to and fro, means to compare the input and output currents of this particular frequency, and phase adjusting means automatically actuated by said comparing means.

23. The method of compensating for variation of phase relations in a multiplex carrier current signaling system, which consists in transmitting one of the frequency components of the system once to and fro, com paring its input and output for phase, and adjusting the phase for all frequencies by means of this comparison.

24. In 'a multiplex carrier current signaling system, means for generating carrier currents of various frequencies and super- 1 posing them on a transmission line, means to modulate certain of these carrier currents in accordance with messages to be transmitted, and means to apply one of these carrier currents for phase regulation of the 1 system.

25. In a multiplex carrier current signaling system, means for generating carrier currents of various frequencies and superposing them on a transmission line, means to modulate certain of these carrier currents in accordance .with messages to be transmitted, and means to apply one of these carrier currents toeffect phase regulation for all of said currents.

26. In a multiplex carrier current system means for generating carrier currents of various frequencies and superposing them on a transmission line, means to modulate certain of these carrier currents in accord- 125 ance with messages to be transmitted, means to a ply one of these carrier currents to sync ronize the receiving apparatus of the system, and means to apply current of the same frequency to compensate for phase variations of transmission on the line.

27. A conductor system for transmitting currents of various frequencies, said system being subject to changes of condition tending to change the phase relations among the various frequencies, means responsive to such changes, and automatically adjustable compensating means controlled thereby to keep the said phase relations constant.

28. A conductor system for transmitting currents of various frequencies, said system bein subject to changes of condition tending to c ange the phase relations among the various frequencies, means responsive to such chan es and compensating means controlled thereIoy to keep the said phase relations constant.

29. A conductor system for transmitting an alternating current of several components, said system being subject to changes of condition tending to change the phase relations of said components at the receiving end, means responsive to such changes and com pensating means controlled thereby to keep the said phase relations constant.

30. In a multiplex carrier current system subject to changes of condition tending to change the phase relations among the elementary currents of the system, means responsive to such changes, and automatically adjustable compensating means controlled thereby to maintain the phase relations unchanged at the receiving end.

31. In a carrier current signaling system requiring a local generator at the receiving end to generate a current of carrier frequency to cooperate-in receiving, means to synchronize the local generator, means to regulate the transmission level of the system, and means to sift out and apply a particular component of the transmitted current to govern said synchronizing means and said regulating means.

32. In a multiplex carrier current system, adjustable means to vary a component of the propagation constant of the system, means to compare a current before and after transmission to test changes in a component of the propagation constant, and means operated by such comparison to actuate said adjustable means.

In testimony whereof, I have signed my name to this specification this 27th day of February 1924.

HARRY NYQUIST. 

